There is increased interest in implantable drug delivery systems to deliver therapeutic fluids to targeted internal tissues such as the inner ear. Drug eluting electrode leads with cortico steroids have been used successfully in the past with cardiac pacemaker electrodes to reduce the contact impedance. In addition, silicone elastomer loaded with a pharmacological agent has been used as an eluting structure in several applications such as birth control, vascular injury treatment, and stents. There also have been attempts to deliver medicine to the inner ear, for example to promote healing after implantation of cochlear implant electrode.
But materials that release a therapeutic substance do not necessarely have a desirable linear release rate and/or may not be refillable (e.g. NuvaRing® birth control device). Large complex implantable drug delivery pumps (e.g. from tricumed Medizintechnik GmbH) are known for implantation in body regions such as the abdomen for delivering significant amounts of therapeutic fluids into the circulatory system. However this technology is designed to deliver relatively large amounts of drugs in body locations which are less fragile and which allow greater implant dimensions than the inner ear.
In US 2009/062896 A1, the inventor describes a nonlinear release profile as illustrated in his FIG. 13. His FIG. 16 shows that this release profile is achieved by loading different forms of the drug dexamethasone, such as dexamethasone salt and dexamethasone base, into a storage lumen.
WO0241666 describes an electrode carrier having a drug impregnated bioresobrable gel that when implanted in a patient releases the drug over time. During manufacture, the electrode must be soaked in the liquid drug for long enough to absorb the chemical. Then the liquid must be dried out for packaging and shipment, and when the electrode is implanted, it absorbs fluid and refoms the gel which then releases the drug over time.